Search

Biohydrogen production from various organic wastes, wastewaters and biomass has been widely studied due to the higher production rates and fundamentals and technologies have also been well developed and heavily documented through diverse laboratory-scale bioreactors. Recently, research has been geared to the concomitant production of biohydrogen and methane which is so called “biohythane”. One-stage and two-stage (bio-H2 + bio-CH4) methods are the main biohythane production methods and this field of research for probing into green biofuels is gradually gaining ground. In this paper, the salient aspects of biohythane research at the present time are revisited and the research success and latent promise of biohythane are highlighted based on the findings of the relatively few publications in this area.

This review analyses the relevant studies which focused on hydrogen synthesis by dark fermentation of galactose from macroalgal biomass by discussing the inoculum-related pretreatments, batch fermentation and inhibition, continuous fermentation systems, bioreactor designs for continuous operation and ionic liquid-assisted catalysis. The potential for process development is also revisited and the challenges towards suppressing glucose dominance over a galactose-based hydrogen production system are presented. The key challenges in the pretreatment process aiming to achieve a maximum recovery of upgradable (fermentable) sugars from the hydrolysates and promoting the concomitant detoxification of the hydrolysates have also been highlighted. The research avenues for bioprocess intensification connected to enhance selective sugar recovery and effective detoxification constitute the critical steps to develop future red macroalgae-derived galactose-based robust biohydrogen production system.

Endosulfan is a highly polluting and toxic pesticide which has been used in many areas globally to control pests in view to improve productivity. Concomitantly, endosulfan has also been associated with many cases of environmental pollution and various types of irreversible metabolic dysfunctions in living organisms both on lands and in waters. Subsequently, since over the last three decades, several endosulfan remediation methods have been studied and many are gradually bringing hope towards efficient clean-up. This article specifically reviews endosulfan degradation and endosulfan removal by discussing the recent findings reported and the trends observed in studies reporting bacterial and fungal bioremediation, photocatalytic degradation, adsorption and membrane separation processes. The salient observations from this review are: there are many bacterial species which degrade endosulfan isomers with relatively high efficiencies; many studies indicate the merits of plants in phytoextracting and accumulating endosulfan but the identification of endosulfan hyperaccumulators remains; photocatalytic systems involving one or two metals also bring about significant endosulfan degradation but issues related with variations in rates of reactions, catalyst deactivation due to fouling, intricacy of metal-based nanocatalyst structures and their complex fabrication methods and lack of control of morphology of the nanosized structures have to be addressed; and membrane retention systems specifically treating endosulfan-contaminated aqueous media are scanty and more analysis is also needed to optimize the shear force-membrane structural integrity-membrane stability rapport of the membranes being developed. In the end, a number of research and development avenues which need further attention and probing towards the development of suitable endosulfan-remediation routes are pointed out. Post-print / Final draft

The green approach of the one-pot enzyme-assisted biomass deconstruction for the production of biofuels and high-value added chemicals in the presence of combined ionic liquids with metal nanoparticles (CILMNPs) process is receiving more interest in biomass-to-energy research. This paper gives a succinct overview of the recent applications of CILMNPs in the pretreatment of lignin-based biomass for macrocellular deconstruction at the one-pot scale and then holistically addresses the multifarious research hurdles, challenges and prospects which have to be addressed to achieve the green merits on a larger scale of processing. Once the one-pot green metrics will be matched by their corresponding process metrics, the potential for pilot-scale production and eventually industrial utilization of CILMNPS will take good shape. Furthermore, such process scale-up campaigns using CILMNPS for biomass depolymerization will have to be robustly designed for an effective and efficient application by selecting bioprocesses involving enzymatic hydrolysis, saccharification and deoxygenation/hydrodeoxygenation routes operated under continuous regimes. These tasks will demand considerable applied research efforts in the form of process intensification and optimization both at the one-pot scale and for prospective large-scale bioprocessing units.

Three abundant coffee residues (green coffee powder, parchment and defatted cake) and sugarcane vinasse were co-digested under thermophilic anaerobic conditions. A pilot plant was set-up and operated under optimized conditions using mesophilic sludge seed to produce biohydrogen. The initial conditions were acidogenic regimes (pH 5.0–6.5) followed by methanogenic conditions (pH 6.5–8.0). Results indicated the concomitant generation of biohydrogen and biomethane (termed biohythane) from the coffee residues. The green coffee powder bioreactor produced a hydrogen-rich biohythane for the first 15 days with a maximum yield on day four (31.45% hydrogen). Results also suggested that start-up of the biosystem reached the methanogenic stage in only 20–25 days and produced methane yields as high as 0.14mlCH4/gVSadded. For the co-digestion of defatted cake and vinasse, the only gas of interest produced was biohydrogen 32% vol./vol. between the 9th and 32nd day. Anaerobic co-digestion of parchment and vinasse produced biohythane at an average yield of 0.21mlCH4/gVSadded.

The effects of microwave irradiation on the digestibility and biogas production of cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) leaves were investigated using biochemical methane potential (BMP) assays. Cow dung was utilised as inoculum. Different microwave powers (87.5, 175 and 350 W) were applied in a first set of runs for 15 min. The second set consisted of 20, 25 and 30 min irradiation at 350 W. Based on ANOVA analysis (α = 0.05), biogas production was significantly higher for the irradiated substrates compared to controls. The peak biogas production was 700 ml for 36 days HRT for 350 W/25 min. Peak COD, SCOD, volatile and total solids removals were 54.84%, 39.08%, 34.60% and 71.96%, respectively. Phosphate and total nitrogen increased significantly. Cumulative biogas production data fitted the modified Gompertz equation well. The highest biogas yield was 0.271 L/g VSremoved at a 350 W microwave irradiation for 30 min.

A sustainable expansion of corn-based and sugarcane-based ethanol production could induce food safety and also decrease the Southern Brazilian Amazon’s extensive cattle farming and deforestation of new pasture areas. The present work aims to evaluate a technological prospect regarding the strategies and market potential of bioenergy and bio-products generation for a corn-based production system. A ‘Strategic Foresight’ approach was formulated and thoroughly analyzed. Overall, it showed that productivity improvement of livestock could be accomplished, and light vehicles’ energy demand using anhydrous and hydrous ethanol could also be enhanced. The results demonstrated that greenhouse gas emissions from a ‘Corn-to-Ethanol’ production system are smaller than the conventional Mills. The Foresight analysis identified that the positive energy balance from ethanol provides more energy than its industrial consumption. ‘Corn Ethanol’ production processes are integrated in six (6) “Flex Mills” in Brazil by taking advantage of the existing installations for sugarcane processing with a production ranging from 250 to 500 million liters/year. The State of Mato Grosso shall have twelve (12) Ethanol Mills in “Full” operation until 2021. The SWOT analysis in this study revealed that: the economy's development could generate direct and indirect jobs, potentially supporting the energy transition to a low-carbon economy through the valorization of agricultural and livestock products, and thus allowing the expansion of confined livestock, pig, and fish farming. Finally, the Strategic Foresight showed the multi-tiered importance of technological application and cooperation in the agro-industrial sector.

Biohydrogen production from lignocellulosic biomass (LCB) is an active research area. Several workers have tested a number of substrates under different operational conditions and brought forward the many positive process performance features and identified the main sources of inhibition. This review analyzes selected fermentative biohydrogen production processes by revisiting the core biohydrogen production performances in terms of gas production rates and yields and equally addresses the options for process enhancement by the application of through pretreatment methods and detoxification of process inhibitors. In addition, the issues related to continuous biohydrogen operation in different reactor configurations are highlighted. Lastly, future avenues of research which may be engendered and engineered to enhance the biohydrogen generation and process biokinetics are discussed. This review intends to provide the fundamental understanding of biohydrogen production and provides a perspective on future developments in this area of applied research.

The objective of this study was to evaluate the effects of sonication on the biogas production dynamics of sugarcane straw and vinasse in an anaerobic digestion. Two different ultrasound pretreatments were evaluated namely 180 W of ultrasonic power irradiated at 37 kHz for 30 min (PBU) and 800 W of ultrasonic power irradiated at 19 kHz for 15 min (PSU). Significant differences were observed in the biogas compositions of the PBU and PSU pretreatments and their respective controls. A continuous increase in methane concentration of the biohythane (biohydrogen and methane combined) was recorded in the PBU reactors (60–80% by volume). The main effect of ultrasound pretreatment was on the composition biohydrogen, methane and carbon dioxide (biohythane) produced.

Excess consumption of energy by humans is compounded by environmental pollution, the greenhouse effect and climate change impacts. Current developments in the use of algae for bioenergy production offer several advantages. Algal biomass is hence considered a new bio-material which holds the promise to fulfil the rising demand for energy. Microalgae are used in effluents treatment, bioenergy production, high value added products synthesis and CO2 capture. This review summarizes the potential applications of algae in bioelectrochemically mediated oxidation reactions in fully biotic microbial fuel cells for power generation and removal of unwanted nutrients. In addition, this review highlights the recent developments directed towards developing different types of microalgae MFCs. The different process factors affecting the performance of microalgae MFC system and some technological bottlenecks are also addressed.

Hydrogen production from lignocellulosic biomass (LCB) using dark fermentation is an interesting research niche being developed over the last decade. This review analyses the relevant studies which focused on biohydrogen production from LCB using dark fermentation techniques in terms of substrate characterization, bottlenecks associated with the pretreatment and its subsequent utilization, possible remedies for the scale-up of the most adapted processes and finally the prospects and suggestions which may be envisaged. Studies dealing primarily with the utilization of raw and pretreated LCB have been assessed in terms of biohydrogen production performance for production rate and yield. Energy production analysis and prospecting of suitable cellulosic biomass and efficient cellulolytic microbes have been elucidated towards better cellulose hydrolysis and efficient conversion of LCB to H2 in addition to process economics.

Over the last couple of decades, academic research on adsorbents has been flourishing. The preparation, functionalization, and adsorption performance evaluation have grown explosively. Novel adsorbents have demonstrated excellent capabilities to remove metal ions and organic contaminants from aqueous environments having different physicochemical conditions. This article presents gaps and potential research possibilities related to economic assessment, benchmarking of synthetic real wastewaters, adsorptive (component) additivity, constraints of process scale-up, process intensification, and modeling, simulation and optimization of large-scale adsorption-based water remediation systems. These discussions foster fresh ideas and investigations in the cognate science and engineering disciplines so that industrial applications of novel adsorbents for innovative water treatment matures both technically and cost-effectively.

The aim of the study was to investigate the effects of carton in the composting process of mixed vegetable wastes using an experimental composter of capacity 80L. Three different mixes were set-up (Mixes 1, 2 and 3) which consisted of vegetable wastes, 2.0kg paper and bulking agents, vegetable wastes, 1.5kg carton and bulking agents, vegetable wastes, 4.5kg carton and bulking agents, respectively. Temperature evolution, pH trends, moisture levels, respiration rates, percentage volatile solids and electrical conductivity were monitored for a period of 50days. The system remained under thermophilic conditions for a very short period due to the small size of the reactor. The three mixes did not exceed a temperature of 55°C, where sanitization takes place by the destruction of pathogens. The highest peak of CO2 evolution was observed in Mix 2 indicating that maximum microbial degradation took place in that mix.

The agricultural and food industry sectors play essential roles in the global economy, but also generate significant amounts of wastes every year associated to their activities, which require an appropriate management. As an alternative, agro-industrial by-products can be used for obtaining valuable compounds such as amino acids, phenolic compounds, water-soluble sugars, organic acids, methane and oils, among others. Several processes have been developed for obtaining such compounds from by-products and residues, among of which the subcritical and supercritical water technologies are considered as green alternatives. This review presents a concise assessment of the research findings reported from 2001 to 2020 on the subcritical and supercritical water extraction and hydrolysis of protein-based substrates to obtain amino acids, addressing aspects such as: economic relevance of protein and amino acids, main routes for protein extraction, influence and interactions of the main reaction parameters and conditions. Protein aggregation-disaggregation and a comparison of selected extraction arrangements, reactor configurations, and finally, future research perspectives are also discussed.

The hydrothermal pretreatment route is gaining research interest as a potentially green method for deconstructing lignocellusic biomass. Based on the relevant literature, the conversion of biomass into platform chemicals or energy carriers through hydrothermal processes has been found to be advantageous by reason of enhanced process performance, while being environmentally friendly and technologically innovative. In this review, an assessment has been made of recent research findings and reservations in regard to the synthesis of subcritical and supercritical hydrolysates and the production of platform chemicals namely ethanol, butanol, furfural, hydroxymethylfurfural, lactic acid, levulinic acid and its derivatives, succinic acid, sorbitol, and xylitol. This review also proposes a number of future research-oriented directions to harness the findings of primary research-oriented efforts for developing technically and economically feasible large-scale systems.

Heavy metals released from industrial activities pose a significant threat to the environment and public health due to their reported toxicity even at trace levels. Although there are several available methods to treat or remove heavy metals from water and wastewater, the research focuses on development of technological solutions which sound environmental friendly and economically feasible, able to reduce the costs and maximize the efficiency. In this framework, the biosorption process, which uses cheap and non-pollutant materials, may be considered as an alternative, viable and promising, technology for heavy metal and metalloid ions sequestration and ultimately removal technology in the waste water treatment. However, there is as yet little data on full-scale applications for the design and testing of adsorption units using single biosorbents and their combinations to sequester heavy metal ions from multi-metal systems. Immediate research and development is hence earnestly required in this specific direction to further make progress this blooming technology and widen its scope of application to real situations needing heavy metal pollution remediation. This review provides a comprehensive appraisal of the equilibrium modeling of a number of biosorption processes as well as the structural, chemical and morphological modifications and activation of biosorbents. Further the relative merits of the methods used to recover sequestered heavy metal ions and regenerate biosorbents through desorption routes and their future applications are discussed.

The kinetics, adsorption isotherms, thermodynamics and spectroscopic analyses of the removal of the anthraquinone dye, Alizarin Red S by adsorption onto mustard husk were studied. Batch adsorption experiments were conducted using synthetic aqueous solutions and the effects of initial dye concentration, initial pH of solution, adsorbent dose and temperature were investigated. The mustard husk adsorbent was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy and through the determination of pH zpc . The equilibrium adsorption data fitted very well to the Freundlich model and this provided evidence of multilayer adsorption of the dye molecules onto the active sites on the biosorbent. The kinetic studies showed that the process was quite rapid and 90% of equilibrium capacity was achieved within 80 min. The process followed the pseudo-second-order kinetic model with a k 2 value of 0.094 g/mg min for an Alizarin Red S concentration of 25 mg/L. Positive Δ H ° and negative Δ G ° were indicative of the endothermic and spontaneous nature, respectively, of Alizarin Red S removal by adsorption onto mustard husk biomass.

Due to the excellent chelating properties of aminopolycarboxylic acid (APCAs), they can be used for the removal of metals from contaminated waters. This paper reviews the research results obtained for both commercial and self-prepared adsorbents functionalized with four most common APCAs: iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The structural characteristics and unique metal binding properties of these chelating adsorbents are presented. The theory of the adsorption phenomena is discussed based on the kinetics of adsorption, equilibrium adsorption isotherm models, and thermodynamic models. The most important applications of APCA-functionalized adsorbents are also described. APCA-functionalized adsorbents are found to be highly promising materials for metal removal from contaminated waters.

The Port Louis Harbour is the sole port in Mauritius and handles 99% of cargo entering the island. The port area is subject to a wide range of port installations handling, processing and storing a wide range of cargo ranging from petroleum products, coal, cement, edible oil, heavy oil, molasses, wheat, bitumen to fertiliser manufacturing. This study integrated procedures of ISO14001 and was carried out in the context of the UNEP GEF WIO–Lab Solid Wastes Demo Project during the period April 2009 to May 2010. An inventory of the wastes generation and flow from ships and within the industrial port area was conducted, and on basis of the results obtained, an environmental pollution prevention and protection program was developed to eventually assist in the setting up of a Port Waste Management System (PWMS) at the Port Louis Harbour. The PWMS identified the significant environmental aspects and impacts, structure of the organisation, distribution of responsibilities, needs for training, objectives and targets as well as the operational control measures. At the end of the study, suggestions on how to improve the port’s environmental performance with regards to waste management were recommended.

Atrazine is a widely used herbicide for controlling weeds on both agricultural and nonagricultural land, which is equally detected in water supplies beyond safe concentrations. Although the presence of atrazine metabolites is an indication of herbicide degradation, some of them still exhibit toxicity, greater water solubility and weaker interaction with soil components than atrazine. Hence, studies with atrazine in the environment are of interest because of its potential to contaminate drinking water sources. Data on atrazine availability for transport, plant uptake, and microbial degradation and mineralization are therefore required to perform more comprehensive and realistic environmental risk assessments of its environmental fate. This review presents an account of the sorption-desorption phenomenon of atrazine on soil and other sorbents by revisiting the several mechanisms of atrazine-sorbent binding reported in the literature. The retention and transport of atrazine in soils; the influence of organic matter on atrazine sorption; the interactions of atrazine with humic substances, atrazine uptake by plants, atrazine bioccumulation and microbial degradation; atrazine transformation in composting environments; and finally atrazine removal by biosorption are discussed.

Efficient compost production requires a thorough understanding of the process dynamics in terms of the feedstock materials used and the interactions of the physical properties involved. The main properties affecting the composting process are temperature, moisture content, bulk density, porosity and oxygen availability. In this study, the correlations between a selected set of physical properties of a batch-composting matrix were determined. The key physical changes in the composting materials for a blend of woodchips, chicken manure and mixed green vegetables have been monitored during a 36-day composting period in a 200-L rotary drum. The daily measurements conducted on the solid samples included temperature, pH, volatile solids, bulk density, moisture content, free airspace and substrates particle density while the carbon dioxide release was monitored weekly using jar respiration tests. The results from the compost process monitoring were a maximum temperature rise to 66.3 °C over the first 3 days, a marked decrease in free airspace from 76.3% to 40.0% at the end of the process, a variation in average composting material particle density from 1097 kg/m3 to 2325 kg/m3, and an increase in wet bulk density from 255 kg/m3 to 628 kg/m3. Correlations developed among free airspace, wet bulk density, dry bulk density and wet moisture content were in agreement with previously determined equations from literature. Free airspace varied linearly with both dry and wet bulk densities (R2 value of 0.89 and 0.95, respectively) while the free airspace–wet moisture content profile followed a fourth degree polynomial trend with a correlation coefficient of 0.63.

This article has been withdrawn at the request of the author(s) and/or Editor. The Publisher apologises for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.